1. Field of the Invention
The present invention relates to an inertial force sensor for detecting the acceleration and angular velocity acting on a displaceable object, and relates particularly to an electrostatic capacity-type acceleration sensor that electrically detects the acceleration from the capacitance change of a capacitor.
2. Description of the Prior Art
An electrostatic capacity-type acceleration sensor comprises an immobile fixed electrode and a displaceable electrode that is displaced by an inertial force of acceleration. Because the dielectric constant between the fixed electrode and displaceable electrode is constant, the electrode distance between the fixed electrode and displaceable electrode changes with the displacement of the displaceable electrode, and the capacitance of the capacitor formed by a dielectric body between the fixed electrode and displaceable electrode changes. This capacitance change makes it possible to detect acceleration by detecting the capacitance change using a detection circuit.
The detection circuit for detecting acceleration using an electrostatic capacity-type acceleration sensor as described above is typically made from an application-specific integrated circuit (ASIC) or other integrated circuit (IC) separately from the electrostatic capacity-type acceleration sensor. However, the capacitance change caused by an inertial force of acceleration in this electrostatic capacity-type acceleration sensor is small, and the detection circuit must therefore detect acceleration from this small change in capacitance. The electrostatic capacity-type acceleration sensor and detection circuit are also connected through the wiring pattern of the circuit board and the detection result is therefore affected by the parasitic capacitance of the wiring pattern. This makes it difficult for the detection circuit to accurately detect the capacitance of the electrostatic capacity-type acceleration sensor.